The performance of many devices, such as laser printers and optical memories, can be improved with laser arrays having independently controlled lasing elements. For example, laser printers which use an array of lasing elements can have higher printing speeds and better spot acuity than printers that use only a single lasing element. In many applications it is important that the array's lasing elements be accurately positioned and oriented.
Monolithic laser arrays usually output light beams with the same wavelength. Typically, that wavelength can only be varied over a small range. However, in some applications, including color printing, it is desirable to output multiple wavelengths that span a wide range; for example, from the infrared through the visible. In color printing this enables one to match the laser output characteristics to photoreceptor response windows, or to separate overlapping laser beams by the use of dichroic filters. In some applications it may be desirable to emit multiple laser beams with different polarizations or spot profiles. Finally, it is almost always desirable to have low electrical, optical, and thermal crosstalk between lasing elements.
As compared to present day monolithic laser arrays, nonmonolithic laser arrays can provide a greater range of laser beam characteristics (such as wavelength and polarization) and have lower electrical, optical, and thermal crosstalk. Thus, nonmonolithic laser arrays are frequently preferred.
A nonmonolithic laser array typically consists of a plurality of individual laser diodes mounted on a support. Since in many applications the output laser beams must be accurately spaced, the supports should enable accurate positioning of the lasing elements, while not detracting from the advantages of nonmonolithic laser arrays.
Prior art nonmonolithic semiconductor laser arrays usually use planar supports. These planar laser arrays have a major problem with how close the emitted laser beams can be spaced. This follows because a lasing eiement's laser stripe (the source of the laser beam) is generally placed at the center of the lasing element to avoid damage during the cutting of the wafer from which the lasing element is produced. Thus, in the prior art laser stripes could not easily be spaced any closer than the width of a lasing element if they are placed on a common planar substrate.
Kato et al. in U.S. Pat. No. 4,901,325 teach a non-planar nonmonolithic laser array suitable for use with closely spaced lasing elements. A simplified view of that support in a nonmonolithic laser array is shown in FIG. 1. While the support 10 (with a spacer 12) enables the lasing elements 14 to be spaced within microns, absolute control of the lasing element spacing (how close the lasing elements are to their desired location) is not provided for. Further, the orientations of the lasing elements are not rigidly controlled.
Thus, there exists a need for methods and devices that enable close, accurate spacing of lasing elements in a nonmonolithic laser array without excessive thermal, optical, and/or electrical cross-talk. Such methods and devices are even more desirable if they permit the accurate orientation of the lasing elements.